NASAL CAVITIES 315 



conjunctiva ; through the various apertures, with the delicate 

 lining membrane of the air-cells which open into the nasal 

 cavity, and, through the choanse, with the pharyngeal mucous 

 membrane. On the lateral wall, as on the septum, the 

 muco- periosteum is separable into an upper, olfactory, and 

 a lower, respiratory portion ; but the subdivision cannot be 

 appreciated by the naked eye, for the one district passes 

 into the other without any sharp line of demarcation. The 

 olfactory region comprises merely the region of the upper 

 concha ; the respiratory region includes the middle and inferior 

 conchae, the middle meatus, the inferior meatus, and the atrium. 

 On the lower part of the lateral wall the muco-periosteum 

 is thick and spongy, more particularly over the lower borders 

 and posterior extremities of the middle and inferior conchae, 

 where the membrane presents an irregular surface and forms 

 soft, bulging cushions. The spongy condition is due to the 

 presence of a rich venous plexus, the vessels of which run, 

 for the most part, in an antero-posterior direction. In the 

 region of the inferior concha, the veins are so numerous 

 that the muco-periosteum assumes the character of cavernous 

 tissue, and is sometimes spoken of as the "erectile body." 

 When turgid with blood it swells out and obliterates the 

 interval between the concha and the septum. The muco- 

 periosteum of the floor, meatuses and atrium, is smoother 

 than, and not so thick as, that over the conchae. Every- 

 where, numerous mucous glands are embedded in it, and 

 the minute punctiform orifices of the ducts are visible to 

 the naked eye. In the olfactory region the lining membrane 

 of the nose, in the fresh state, is of a yellowish colour, and 

 it is softer and more delicate than in the respiratory part. 



The great vascularity of the mucous membrane of the nose 

 is, doubtless, for the purpose of moistening and raising the 

 temperature of the inspired air. 



Nerves and Vessels on the Lateral Wall of the Nasal 

 Cavity : 



Nerves of Smell, . Olfactory nerves. 



Lateral nasal branches of anterior ethmoidal. 



!I. 

 2. Nasal branch of anterior superior alveolar. 

 : 



Nerves of Common f 3. Posterior superior nasal branches from spheno- 

 Sensation, . .^ palatine ganglion and from the nerve of the 



pterygoid canal. 



[.. Two posterior inferior nasal branches from the 

 anterior palatine nerve. 



